[fix] Save document settings before activating USBMS (#6713)
[fix] Save document settings before activating USBMS (#6713)

As things were, when I activated USBMS, any bookmarks recently added and not yet stored in the sidecar file would be lost after returning to the reader. These changes fix that.
koreader/koreader,poire-z/koreader,Hzj-jie/koreader,koreader/koreader,poire-z/koreader,Frenzie/koreader,NiLuJe/koreader,Markismus/koreader,Frenzie/koreader,pazos/koreader,NiLuJe/koreader,mwoz123/koreader